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Borewell installation in Tumkur: Life of well?

We want to install a borewell in Tumkur town (70 kms from bangalore). We already have a borewell (dug upto 400 feet) which has dried up (within 3 years). Now geologist says that just 80 feet from original bore , there is a water source at 650 feet. Borewell driller person says that inserting a iron pipe for 150 feet is what they do, though they drill until they hit the water source (~ 700 or 800 feet).

On the other hand, in Tamilnadu (Cauvery delta region - Thanjavur), borewells are installed even upto 400 feet or more. they are working for more than 10 years now without problem. they use PVC pipe.

In TN, I learnt that borewell drillers use PVC pipes (pipes with cuts along its length) and encased in another outer pipe. Moreover it seems they use jally packing. These steps are told to help filtering water so that the bored area does not get covered over time.

In Tumkur, when we enquired borewell drillers say that Tumkur is silt area and hence borewell anyway won't last long and they don't use such techniques.

Can someone help me with this problem?

is it not possible to do a borewell which will last for atleast 10 years in tumkur? what kind of borewell should be done?

Ponni K

ponni.k@nsn.com

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Comments

1.

As you said, that Borewell which last for 10 years, is due to availability of water in that region, In your case is that it did not last for 3 years, Mere pumping out water would make the water table to go down in that location and got dried, So I request you to adhere to Rain Water Harvesting Technique in future, So that borewell would not dry in a short period and it is also not so expensive.

Slit has draw back, it is iron pipe to be correctly placed at the bottom of Borewell, if it correctly not placed then the silt may enter into borewell and suppress the flow of water.

Regards

Baskar
Chennai,

2.

As unconsolidated formations such as sand, silt and clay extend to great depths in the Thanjavur region of Cauvery delta, it is feasible (and also necessary) to use rotation method of drilling to construct tube wells using bentonite lining and later installing blank casing pipe at the top and slotted casing pipe surrounded by gravel pack against the water-bearing formation.

Contrary to this, the Tumkur area comprises of hard rocks where bore wells rather than tube wells are feasible. They are drilled by rotary percussion method using Down-The-Hole (DTH) Hammer rigs. Blank casing pipe is installed at the top to prevent entry of loose material into the bore well. No casing pipe is inserted in the bottom where hard rock having one or more pipeline-like water-bearing fractures within it.

Although Ponni states that his 3-year old 400-feet bore well is now dry, he has not given reasons why it became dry. It is possible that the well became dry due to decline of groundwater level or bore well getting filled with silt.

From Ponni's description of the local drillers' experience, any Tumkur bore well becomes unserviceable due to silt accumulation in around three years time and casing pipe can be installed in a bore well to a maximum depth of 150 feet. To understand about Tumkur groundwater better, it is necessary to have the following additional information.

1. How much was the reduction of bore well depth as a result of silting?

2. How much was the reduction in the depth to water level before and after the bore well became unserviceable?

3. If the bore well got silted up and became dry, has any attempt made to flush it to make it productive?

4. What is the exact source of silt entering the bore well? Has it entered from the annular space between the casing pipe and the top formation of the bore well, or from the formation immediately below the casing pipe or from some greater depth?

5. Are there no long-lasting bore wells and drillers to drill such wells in the Tumkur area?

Dr. R. Jagadiswara Rao
Former Professor of Geology
Sri Venkateswara University
Tirupati, AP 517502
rjagadiswara@gmail.com

Dr. R. Jagadiswara Rao, Professor of Geology Retired, Sri Venkateswara University, Tirupati, AP 517502, India rjagadiswara@gmail.com

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